U.S. patent application number 09/747854 was filed with the patent office on 2002-01-17 for coating composition for metallic substrates.
Invention is credited to Lane, Matthew T., Newton, David L..
Application Number | 20020006996 09/747854 |
Document ID | / |
Family ID | 25006923 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006996 |
Kind Code |
A1 |
Lane, Matthew T. ; et
al. |
January 17, 2002 |
Coating composition for metallic substrates
Abstract
The invention provides a coating composition for use with
metallic substrates that provides a unique balance of required
properties. In particular, the coating composition of the invention
simultaneously provides desirable levels of adhesion to metal,
sandability without the production of harmful dust, corrosion
resistance, and recoatability. The coating composition of the
invention comprises a polyurethane or epoxy/amine film-forming
component, and a corrosion protection component consisting of
aluminum selected from the group consisting of nonleafing aluminum
pigments, the corrosion protection component being present in the
composition in an amount effective to prevent corrosion of the
substrate. A cured film of the coating applied to a steel substrate
has a pass rating after 480 hours in salt spray per ASTM B117.
Inventors: |
Lane, Matthew T.; (Bowling
Green, OH) ; Newton, David L.; (Toledo, OH) |
Correspondence
Address: |
BASF CORPORATION
PATENT DEPARTMENT
26701 TELEGRAPH ROAD
SOUTHFIELD
MI
48034-2442
US
|
Family ID: |
25006923 |
Appl. No.: |
09/747854 |
Filed: |
December 22, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09747854 |
Dec 22, 2000 |
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09599693 |
Jun 22, 2000 |
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09747854 |
Dec 22, 2000 |
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09599695 |
Jun 22, 2000 |
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Current U.S.
Class: |
524/441 |
Current CPC
Class: |
C08L 67/00 20130101;
C08G 18/4684 20130101; C09D 5/002 20130101; C08G 18/3885 20130101;
C09D 175/04 20130101; C09D 175/04 20130101; C08L 67/00 20130101;
C09D 5/103 20130101; B05D 3/12 20130101; C08L 67/00 20130101; B05D
7/16 20130101; C08L 75/04 20130101 |
Class at
Publication: |
524/441 |
International
Class: |
C08K 005/49; C08K
003/08 |
Claims
What is claimed is:
1. A sandable and recoatable coating composition for preventing
corrosion of a metallic substrate, the composition comprising a
film-forming component comprising a film-forming polymer and a
crosslinking agent, wherein the film-forming polymer has functional
groups selected from the group consisting of active hydrogen
containing groups, epoxide groups, and mixtures thereof, and the
crosslinking agent have functional groups selected from the group
consisting of isocyanate groups and amine groups, and a corrosion
protection component consisting essentially of aluminum selected
from the group consisting of nonleafing aluminum pigments and which
is present in an amount effective to prevent corrosion of the
substrate, wherein a cured film of the coating applied to a
metallic substrate has a pass rating after 480 hours in salt spray
per ASTM B117, and is both sandable and recoatable.
2. The coating composition of claim 1 wherein the film-forming
component comprises a film forming polymer comprising an active
hydrogen group containing polymer and an isocyanate functional
crosslinking agent.
3. The coating composition of claim 1 wherein the film-forming
component comprises an epoxy functional film forming polymer and an
amine functional crosslinking agent.
4. The coating composition of claim 1 which is a two component
coating composition wherein the film-forming polymer is in a
polymer component (I) and the crosslinking agent is in a hardener
component (II).
5. The coating composition of claim 1 wherein the corrosion
protection component is present in an amount of from 0.011 to 0.051
weight percent, based on the total nonvolatile film-forming
component of the coating composition.
6. The coating composition of claim 5 wherein the corrosion
protection component is present in an amount of from 0.015 to 0.045
weight percent, based on the total nonvolatile film-forming
component of the coating composition.
7. The coating composition of claim 6 wherein the corrosion
protection component is present in an amount of from 0.020 to 0.040
weight percent, based on the total nonvolatile film-forming
component of the coating composition.
8. The coating composition of claim 5 wherein the corrosion
protection component is a lamellar shaped aluminum pigment.
9. The coating composition of claim 1, wherein the film-forming
component further comprises (I) a first compound having an acid
number of from 70 to 120 mg KOH/g, a hydroxyl number of from 200 to
400 mg KOH/g, a number average molecular weight of from 150 to
3000, and which is the reaction product of (a) at least one
difunctional carboxylic acid, (b) at least one trifunctional
polyol, (c) at least one chain stopper, and (d) phosphoric acid,
and (II) a second compound comprising one or more carboxy phosphate
esters having the formula: 4wherein M is hydrogen, metal, or
ammonium, x is a number from 0 to 3, R is an C.sub.5-C.sub.40
aliphatic group having one or more --COOR.sup.1 groups, wherein
R.sup.1 is H, metal, ammonium, C.sub.1-C.sub.6 alkyl, or
C.sub.6-C.sub.10 aryl.
10. The coating composition of claim 4 wherein polymer component
(I) and hardener component (II) are separated up to at least 10
hours before a first use of a mixture of said first and second
components.
11. The coating composition of claim 10 wherein the corrosion
protection component is in the polymer component (I).
12. A method of preventing corrosion of a metallic substrate,
comprising applying a coating to the metallic substrate, the
coating comprising a film-forming component comprising a
film-forming polymer and a crosslinking agent, wherein the
film-forming polymer has functional groups selected from the group
consisting of active hydrogen containing groups, epoxide groups,
and mixtures therof, and the crosslinking agent have functional
groups selected from the group consisting of isocyanate groups and
amine groups, and a corrosion protection component consisting of
aluminum selected from the group consisting of nonleafing aluminums
and present in the composition in an amount effective to prevent
corrosion of the substrate, and curing the coating to provide a
coated metallic substrate wherein the coated metallic substrate has
a pass rating after 480 hours in salt spray per ASTM B117.
13. A method of making a multilayer coating system, comprising
applying a primer coating composition directly to a metal
substrate, the primer coating composition comprising a film-forming
component comprising a film-forming polymer and a crosslinking
agent, wherein the film-forming polymer has functional groups
selected from the group consisting of active hydrogen containing
groups, epoxide groups, and mixtures therof, and the crosslinking
agent have functional groups selected from the group consisting of
isocyanate groups and amine groups, and a corrosion protection
component consisting of aluminum selected from the group consisting
of nonleafing aluminums and present in the composition in an amount
effective to prevent corrosion of the substrate, and curing the
coating to provide a primed metallic substrate, and applying to the
primed metallic substrate one or more additional coating
compositions, and curing the one or more additional coating
compositions to provide a cured multilayer coating system.
Description
FIELD OF THE INVENTION
[0001] This application is a continuation in part, claiming
priority upon U.S. Ser. No. 09/599,693. The invention relates to
coating compositions for use with metallic substrates and more
particularly to automotive refinish coating compositions intended
for use on metallic substrates, and especially to two component
polyurethane primers which can be sanded and recoated and are
intended for use on steel substrates.
BACKGROUND OF THE INVENTION
[0002] As used herein, "automotive refinish" refers to compositions
and processes used in the repair of a damaged automotive finish,
usually an OEM provided finish. Refinish operations may involve the
repair of one or more outer coating layers, the repair or
replacement of entire automotive body components, or a combination
of both. The terms "refinish coating" or "repair coating" may be
used interchangeably.
[0003] Automotive refinishers must be prepared to paint a wide
variety of materials. Examples of commonly encountered materials
are one or more previously applied coatings, plastic substrates
such as RIM, SMC and the like, and metal substrates such as
aluminum, galvanized steel, and cold rolled steel. Bare metal and
plastic substrates are often exposed as a result of the removal of
the previously applied coating layers containing and/or surrounding
the defect area. However, it is often difficult to obtain adequate
adhesion of refinish coatings applied directly to exposed bare
substrates.
[0004] Among the many factors influencing the degree of refinish
coating/substrate adhesion are the type of exposed substrate, the
presence or absence of adhesion promoting pretreatments and/or
primers, the size of the exposed area to be repaired, and whether
previously applied "anchoring" coating layers surround the exposed
repair area.
[0005] For example, refinish adhesion is particularly challenging
when the exposed substrate is a bare metal such as galvanized iron
or steel, aluminum or cold rolled steel. It is especially hard to
obtain adequate refinish adhesion to galvanized iron. "Galvanized
iron or steel" as used herein refers to iron or steel coated with
zinc. "Steel" as used herein refers to alloys of iron with carbon
or metals such as manganese, nickel, copper, chromium, molybdenum,
vanadium, tungsten and cobalt.
[0006] Refinish operations have traditionally used adhesion
pretreatments to overcome the adhesion problems associated with the
coating of bare metal substrates. Pretreatment as used herein may
refer to either mechanical or chemical alterations of the bare
metal substrate. Mechanical alterations used to obtain improved
adhesion include sanding, scuffing, and the like. Chemical
alterations include treatment of the substrate with compositions
such as chromic acid conversion coatings, acid etch primers and the
like.
[0007] Although such pretreatments have obtained improved refinish
adhesion, they are undesirable for a number of reasons. Most
importantly, pretreatments are inefficient and expensive to apply
in terms of material, time, and/or labor costs. Some chemical
pretreatments also present industrial hygiene and disposal issues.
Finally, the use of some pretreatments such as acid etch primers
may contribute to water sensitivity and/or coating failure under
test conditions of extreme humidity.
[0008] Accordingly, it is highly desirable to eliminate the need
for substrate pretreatment as regards the refinish coating of bare
metal substrates.
[0009] In addition, adhesion to bare metal substrates is improved
when the defect area to be repaired is relatively small and is
surrounded by previously applied coating layers. Such previously
applied coating layers act as an `adhesion anchor` to the refinish
coating. However, many refinish repairs are of a size such that
they lack any surrounding adhesion anchors. Moreover, such
anchoring adhesion may be completely absent when replacement body
parts are painted with a refinish coating.
[0010] Finally, improvements in refinish adhesion to bare exposed
metal substrates must not be obtained at the expense of traditional
refinish coating properties. Such properties include sandability,
recoatability, corrosion resistance, durability, ambient or low
temperature cure, application parameters such as pot life,
sprayability, and clean up, and appearance. Performance properties
such as sandability, recoatability and corrosion resistance are
particularly important for coating compositions intended for use as
primers over steel substrates.
[0011] However, it has been difficult for the prior art to obtain
the proper balance with regard to sandability, recoatability,
corrosion resistance, and metal adhesion requirements.
[0012] Failure to provide adequate corrosion resistance or salt
spray resistance typically manifests as "scribe creep". "Scribe
creep" refers to the degree of corrosion and/or loss of adhesion
which occurs along and underneath film adjacent to a scribe made in
a cured film after the scribed film has been placed in a salt spray
test apparatus. The scribe generally extends down through the film
to the underlying metal substrate. As used herein, both `corrosion
resistance` and `salt spray resistance` refer to the ability of a
cured film to stop the progression of corrosion and/or loss of
adhesion along a scribe line placed in a salt spray test apparatus
for a specified time. Cured films that fail to provide adequate
salt spray resistance are vulnerable to large scale film damage
and/or loss of adhesion as a result of small or initially minor
chips, cuts and scratches to the film and subsequent exposure to
outdoor weathering elements.
[0013] Although urethane coatings have been known to be useful as
refinish primers, they have not achieved the desired balance of
properties.
[0014] In particular, for polyurethane films to provide desirable
salt spray resistance, they have typically relied upon the use of
corrosion protection components containing heavy metal pigments
such as strontium chromate, lead silica chromate, and the like.
Unfortunately, sanding such a film produces dust that is
environmentally disfavored due to the presence of the heavy metal
containing pigments. Since sanding is a necessity for automotive
refinish primers, this disadvantage can render the coating unusable
in most commercial refinish application facilities. Accordingly, it
would be advantageous to provide a coating which can provide
adequate salt spray resistance but which is substantially free of
any heavy metal containing pigments.
[0015] Aluminum pigments have traditionally been used to provide a
desirable metallic or lustrous appearance. For example, the 1977
Federation Series on Coatings Technology teaches that aluminum
pigment containing paints have no specific anti-corrosive effect,
such as is afforded by rust-inhibitive pigments traditionally used
in commercially acceptable metal primers. Indeed, it is further
taught that strontium chromate should be used in combination with
aluminum pigments to provide aluminum containing paints having an
anti-corrosive effect.
[0016] Aluminum pigments, especially leafing aluminums, are known
to produce an apparently continuous film of aluminum metal.
[0017] Barrier pigments, especially platy or platelet pigments have
been known to provide anticorrosive effects.
[0018] However, leafing aluminums and barrier pigments have
traditionally been somewhat disfavored due to recoatability and/or
sanding performance issues. Moreover, the anticorrosive effect of
the coating post sanding can be impaired due to the removal of the
barrier or leafing layer. As a result, the use of aluminum pigments
in primers is to some extent disfavored.
[0019] The prior art has thus failed to provide a coating
composition intended for use as a direct to metal primer which has
commercially acceptable performance properties with regard to salt
spray resistance, sandability, recoatability and adhesion to metal
substrates, especially iron and/or steel.
[0020] Accordingly, it is an object of the invention to provide a
curable coating composition that can be applied directly to a metal
substrate and provides a commercially acceptable level of salt
spray resistance.
[0021] It is a further object of the invention to provide a curable
coating composition which has commercially acceptable performance
properties with regard to direct to metal adhesion and salt spray
resistance and further can be sanded without the production of
environmentally disfavored dust.
[0022] It is a further object of the invention to provide a curable
coating composition which has commercially acceptable performance
properties with regard to direct to metal adhesion, salt spray
resistance, sandability, and further can be recoated with a second
application of the curable coating composition of the invention or
another curable coating composition.
[0023] Finally, it is an object of the invention to provide a
curable coating composition which has commercially acceptable
performance properties with regard to direct to metal adhesion,
salt spray resistance, sandability, and recoatability, especially a
curable coating composition having a film forming component
selected from the group consisting of polyurethane systems and
epoxy/amine systems.
SUMMARY OF THE INVENTION
[0024] It has been found that these and other objects of the
invention have been achieved with the use of a curable coating
composition comprising a film-forming component selected from the
group consisting of polyurethane systems and epoxy/amine systems,
and a corrosion protection component consisting of aluminum
selected from the group consisting of nonleafing aluminum pigments
and present in an amount effective to prevent corrosion of the
substrate, wherein a cured film of the coating applied to a
metallic substrate has a pass rating after 480 hours in salt spray
per ASTM B117, and is both sandable and recoatable.
[0025] In a preferred embodiment of the invention, the aluminum
pigment will be a lamellar shaped aluminum pigment and will be
present in an amount of from 0.011 to 0.051 P/B.
[0026] In a particularly preferred embodiment of the invention, the
film forming component of the invention will be a polyurethane
based coating system comprising a film forming polymer which is an
active hydrogen containing group polymer and an isocyanate
functional crosslinking agent.
[0027] In a most preferred embodiment of the invention, the
polyurethane film forming component will further comprise a
composition comprising (I) an effective amount of a first compound
having an acid number of from 70 to 120 mg KOH/g, a hydroxyl number
of from 200 to 400 mg KOH/g, a number average molecular weight of
from 300 to 700, and which is the reaction product of (a) at least
one difunctional carboxylic acid, (b) at least one trifunctional
polyol, (c) at least one chain stopper, and (d) phosphoric acid,
and (I) an effective amount of a second compound comprising a
carboxy phosphate ester having the formula: 1
[0028] wherein R is an C5-C40 aliphatic group in which one or more
aliphatic carbon atoms are substituted with lateral or terminal
--COOR1 groups, wherein R1 is H, metal, ammonium, C1-C6 alkyl, or
C6-C10 aryl, M is hydrogen, metal or ammonium and x is a number
from 0 to 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The methods of the invention utilize two-component coating
compositions. As used herein, the term "two-component" refers to
the number of solutions and/or dispersions which are mixed together
to provide a curable coating composition. Up until the point of
mixing, neither of the individual components alone provides a
curable coating composition.
[0030] Once mixed, the resulting curable coating composition is
applied to a substrate as quickly as possible. Typically, "as
quickly as possible" means immediately after the mixing of the
separate components or within eight (8) hours from the time the
separate components are mixed, preferably less than one (1) hour
after mixing. In a typical two-component application process the
components are mixed together either (i) at the nozzle of a sprayer
by the joining of two separate carrier lines at the nozzle or (ii)
immediately upstream of the nozzle of a sprayer and then delivered
to the nozzle via a single carrier line. Once at the nozzle, the
mixture is immediately atomized into a mist which is directed at a
substrate which is being coated with a film of the mixture of the
two-components.
[0031] Unlike one-component compositions, two-component
compositions will generally cure in the absence of elevated
temperatures. The individual components (I) and (II) will react
with each other upon admixture to provide a crosslinked product,
most often at ambient temperatures, or more particularly at
temperatures of from 15 to 60.degree. C. and most preferably from
24 to 60.degree. C.
[0032] The coating compositions of the invention comprise a
corrosion protection component that consists essentially of, and
more preferably consists of, one or more aluminum pigments.
Although the composition may contain other filler and/or extender
pigments such as talc, barrites, silicas and the like, such are not
generally considered to substantially contribute to the salt spray
resistance of cured films made from the coating compositions of the
invention.
[0033] Aluminum pigments suitable for use in the instantly claimed
compositions are those aluminum pigments defined as nonleafing
aluminum pigments. Although the prior art has taught that the
leafing aluminum pigments may be superior in regards to possible
anti corrosive effects due to the formation of a barrier-like
layer, it has been found that the use of nonleafing aluminum
pigments is advantageous in the coating composition of the
invention.
[0034] Leafing aluminum pigments have a hydrophobic nature which
causes the pigments to float on the surface of water. When placed
in a coating, the flakes of leafing aluminum pigments will
orientate at or near the surface of the cured film. The flakes are
normally oriented in a parallel overlapping fashion and provide a
continuous metallic sheath.
[0035] In contrast, nonleafing aluminum pigments are distributed
evenly throughout the entire cured film. This distribution is
generally attributed to the lubricants used during the aluminum
pigment manufacturing process. Typically used lubricants are
unsaturated fatty acids such as oleic acid.
[0036] Suitable nonleafing aluminum pigments will have flake
thicknesses of from 0.1 .mu.m to 2.0 .mu.m and diameters of from
0.5 .mu.m to 200 .mu.m.
[0037] Acid-resistant grades of nonleafing aluminum pigments are
particularly preferred.
[0038] In general, the corrosion protection component of the
invention will be present in an amount of from 0.011 to 0.051, more
preferably 0.015 to 0.045, and most preferably from 0.025 to 0.040,
all being based on P/B, i.e., the % by weight based on the total
nonvolatile of the film-forming component, i.e., the total
nonvolatile weight of the film-forming polymer and the crosslinking
agent.
[0039] Coating compositions of the invention will generally have a
pass rating for 480 hour salt spray tests per ASTM B117,
incorporated herein by reference. A pass rating is scribe creep of
less than 3 mils along the edge of the scribe. More preferably, the
coating compositions of the invention will have no more than 2 mils
of adhesion loss along the scribe and most preferably will have
scribe creep of from 0.5 to 1.5 mils. The coating compositions of
the invention will also be free of blistering and rust spots upon
completion of salt spray tests per ASTM B117.
[0040] The two-component coating composition typically comprises a
film-forming component that in turn comprises a film-forming
polymer or binder and a crosslinking agent. The film-forming
polymer is typically in a polymer or binder component (I), while
the crosslinking agent is typically in a hardener component
(II).
[0041] Coating compositions of the invention may comprise any of
the film-forming components used in the refinish coatings industry.
Such coating compositions may rely on air dry lacquer film
formation, film formation via chemical crosslinking, or a
combination thereof Thermosetting films produced by chemical
crosslinking are most preferred.
[0042] Thermosetting coatings of the invention will comprise at
least one film-forming polymer and at least one crosslinking agent.
The film-forming polymer will comprise one or more functional
groups reactive with one or more functional groups on the
crosslinking agent. Examples of functional group combinations
useful for the production of crosslinked coatings include, but are
not limited to, active-hydrogen and isocyanate, epoxide and
carboxylic acid, hydroxyl/carboxylic acid and/or
urea-formaldehyde/melamine-formaldehyde, epoxide and amine, and the
like.
[0043] Although the film-forming polymer may contain any functional
group reactive with the functional group present on the
crosslinking agent, preferably the functional group present on the
film-forming polymer is at least one functional group selected from
the group consisting of hydroxyl, amine, carboxylic acid, epoxy and
mixtures thereof. Especially preferred functional groups for use on
the film-forming polymer are hydroxyl groups and amine groups, with
hydroxyl groups being most preferred.
[0044] Examples of suitable film-forming polymers are acrylic
polymers, polyurethane polymers, polyesters, alkyds, polyamides,
epoxy group containing polymers, and the like.
[0045] Particularly preferred film-forming polymers will be
difunctional, generally having an average functionality of about
two to eight, preferably about two to four. These compounds
generally have a number average molecular weight of from about 400
to about 10,000, preferably from 400 to about 8,000. However, it is
also possible to use low molecular weight compounds having
molecular weights below 400. The only requirement is that the
compounds used as film-forming polymers not be volatile under the
heating conditions, if any, used to cure the compositions.
[0046] More preferred compounds containing reactive hydrogen groups
are the known polyester polyols, polyether polyols, polyhydroxyl
polyacrylates, polycarbonates containing hydroxyl groups, and
mixtures thereof In addition to these preferred polyhydroxyl
compounds, it is also possible to use polyhydroxy polyacetals,
polyhydroxy polyester amides, polythioether containing terminal
hydroxyl groups or sulphydryl groups or at least difunctional
compounds containing amino groups, thiol groups or carboxy groups.
Mixtures of the compounds containing reactive hydrogen groups may
also be used.
[0047] In a most preferred embodiment of the invention, the
film-forming polymer reactable with the crosslinking agent is an
acrylic resin, which may be a polymer or oligomer. The acrylic
polymer or oligomer preferably has a number average molecular
weight of 500 to 1,000,000, and more preferably of 1000 to 20,000.
Acrylic polymers and oligomers are well-known in the art, and can
be prepared from monomers such as methyl acrylate, acrylic acid,
methacrylic acid, methyl methacrylate, butyl methacrylate,
cyclohexyl methacrylate, and the like. The active hydrogen
functional group, e.g., hydroxyl, can be incorporated into the
ester portion of the acrylic monomer. For example,
hydroxy-functional acrylic monomers that can be used to form such
resins include hydroxyethyl acrylate, hydroxybutyl acrylate,
hydroxybutyl methacrylate, hydroxypropyl acrylate, and the like.
Amino-functional acrylic monomers would include t-butylaminoethyl
methacrylate and t-butylamino-ethylacrylate. Other acrylic monomers
having active hydrogen functional groups in the ester portion of
the monomer are also within the skill of the art.
[0048] Modified acrylics can also be used. Such acrylics may be
polyester-modified acrylics or polyurethane-modified acrylics, as
is well known in the art. Polyester-modified acrylics modified with
e-caprolactone are described in U.S. Pat. No. 4,546,046 of Etzell
et al, the disclosure of which is incorporated herein by reference.
Polyurethane-modified acrylics are also well known in the art. They
are described, for example, in U.S. Pat. No. 4,584,354, the
disclosure of which is incorporated herein by reference.
[0049] Polyesters having active hydrogen groups such as hydroxyl
groups can also be used as the film-forming polymer in the
composition according to the invention. Such polyesters are
well-known in the art, and may be prepared by the
polyesterification of organic polycarboxylic acids (e.g., phthalic
acid, hexahydrophthalic acid, adipic acid, maleic acid) or their
anhydrides with organic polyols containing primary or secondary
hydroxyl groups (e.g., ethylene glycol, butylene glycol, neopentyl
glycol).
[0050] Polyurethanes having active hydrogen functional groups are
also well known in the art. They are prepared by a chain extension
reaction of a polyisocyanate (e.g., hexamethylene diisocyanate,
isophorone diisocyanate, MDI, etc.) and a polyol (e.g.,
1,6-hexanediol, 1,4-butanediol, neopentyl glycol, trimethylol
propane). They can be provided with active hydrogen functional
groups by capping the polyurethane chain with an excess of diol,
polyamine, amino alcohol, or the like.
[0051] Although polymeric or oligomeric active hydrogen components
are often preferred, lower molecular weight non-polymeric active
hydrogen components may also be used in some applications, for
example aliphatic polyols (e.g., 1,6-hexane diol), hydroxylamines
(e.g., monobutanolamine), and the like.
[0052] Examples of suitable crosslinking agents include those
compounds having one or more functional groups reactive with the
functional groups of the film-forming polymer. Examples of suitable
crosslinking agents include isocyanate functional compounds and
aminoplast resins, epoxy functional compounds, acid functional
compounds and the like. Most preferred crosslinkers for use in the
coating compositions of the invention are isocyanate functional
compounds.
[0053] Suitable isocyanate functional compounds include
polyisocyanates that are aliphatic, including cycloaliphatic
polyisocyanates, or aromatic. Useful aliphatic polyisocyanates
include aliphatic diisocyanates such as ethylene diisocyanate,
1,2-diisocyanatopropane, 1,3-diisocyanatopropane,
1,6-diisocyanatohexane, 1,4-butylene diisocyanate, lysine
diisocyanate, hexamethylene diisocyanate (HDI), 1,4-methylene
bis-(cyclohexylisocyanate) and isophorone diisocyanate. Useful
aromatic diisocyanates include the various isomers of toluene
diisocyanate, meta-xylenediioscyanate and para-xylenediisocyanate,
also 4-chloro-1,3-phenylene diisocyanate,
1,5-tetrahydro-naphthalene diisocyanate, 4,4'-dibenzyl diisocyanate
and 1,2,4-benzene triisocyanate can be used. In addition, the
various isomers of alpha.,.alpha.,.alpha.',- .alpha.'-tetramethyl
xylene diisocyanate can be used..
[0054] In a most preferred embodiment, the crosslinking agent will
comprise one or more components selected from the group consisting
of hexamethylene diisocyanate (HDI), the isocyanurates of HDI, the
biurets of HDI, and mixtures thereof, with the isocyanurates and
biurets of HDI being particularly preferred.
[0055] Suitable isocyanate functional compounds may be unblocked,
in which case the coating composition should be utilized as a two
component system, i.e., the reactive components combined shortly
before application, or they may be blocked. Any known blocking
agents, such as alcohols or oximes, may be used.
[0056] In a most preferred embodiment of the coating compositions
of the invention, the coating composition will be a two-component
system with the reactive film forming polymer and the crosslinking
agent combined shortly before application. In such an embodiment,
the most preferred coating composition of the invention comprising
the mixture of compounds (I) and (II) will be preferably
incorporated with the film-forming polymer containing
component.
[0057] Hardener component (II) may also comprise one or more
solvents. In a preferred embodiment, component (II) will include
one or more solvents. Suitable solvents and/or diluents include
aromatics, napthas, acetates, ethers, esters, ketones, ether esters
and mixtures thereof.
[0058] Additives, such as catalysts, pigments, dyes, leveling
agents, and the like may be added as required to the coating
compositions of the invention.
[0059] In a most preferred embodiment of the invention, the coating
compositions of the invention will further comprise an adhesion
enhancing composition comprising a mixture of a first compound (I)
and a second compound (II), wherein compound (I) and compound (II)
cannot be the same. It has unexpectedly been found that the
combination of compounds (I) and (II) provides an improvement in
refinish adhesion, i.e., the adhesion of a refinish coating to a
bare exposed metal substrate, which is better than that obtained
with the use of either compound (I) or compound (II) alone.
[0060] Compound (I) is a low molecular weight polyester compound
having both acid and hydroxyl functionality. It will generally have
a number average molecular weight in the range of from 150 to 3000,
preferably from 300 to 1000, and most preferably from 400 to 600.
Compound (I) will generally have a polydispersity of from 1.00 to
2.00, with a polydispersity of 1.50 being most preferred.
[0061] Suitable compounds (I) will also have an acid number in the
range of from 70 to 120 mg KOH/g, preferably from 70 to 100 mg
KOH/g, and most preferably from 70 to 80 mg KOH/g.
[0062] In addition, suitable compounds (I) will have a hydroxyl
number in the range of from 200 to 400 mg KOH/g, more preferably
from 300 to 400 mg KOH/g and most preferably from 330 to 360 mg
KOH/g.
[0063] Compound (I) generally comprises the reaction product of the
reaction of (a) at least one difunctional carboxylic acid, (b) at
least one trifunctional polyol, (c) at least one chain stopper, and
(d) phosphoric acid.
[0064] Examples of suitable difunctional carboxylic acids (a)
include adipic acid, azeleic acid, fumaric acid, phthalic acid,
sebacic acid, maleic acid, succinic acid, isophthalic acid,
tetrahydrophthalic acid, hexahydrophthalic acid, dimer fatty acids,
itaconic acid, glutaric acid, cyclohexanedicarboxylic acid, and
mixtures thereof. Preferred difunctional carboxylic acids (a) are
adipic acid and azeleic acid. Adipic acid is most preferred for use
as difunctional carboxylic acid (a).
[0065] The at least one trifunctional polyol (b) may be branched or
unbranched, but branched trifunctional polyols are preferred.
Examples of suitable trifunctional polyols (b) are
trimethylolpropane, trimethylol ethane, glycerin,
1,2,4-butanetriol, and mixtures thereof. Preferred trifunctional
polyols (b) are trimethylolpropane and trimethylol ethane, with
trimethylolpropane being a most preferred trifunctional polyol
(b).
[0066] The at least one chain stopper will generally be a
carboxylic acid that is different from the at least one
difunctional carboxylic acid (a). Monocarboxylic acids are
preferred. Suitable carboxylic acids (c) will preferably contain
one or more aromatic structures and will preferably contain some
branched alkyl groups. Examples of suitable carboxylic acids (c)
include para-t-butyl benzoic acid, benzoic acid, salicylic acid,
2-ethylhexanoic acid, pelargonic acid, isononanoic acid, C.sub.18
fatty acids, stearic acid, lauric acid, palmitic acid, and mixtures
thereof. Preferred carboxylic acids (c) include para-t-butyl
benzoic acid, benzoic acid, and 2-ethylhexanoic acid, with
para-t-butyl benzoic acid being most preferred.
[0067] Phosphoric acid (d) should be added to the reaction mixture
in an amount of from 0.03 to 0.20, preferably from 0.05 to 0.15,
and most preferably from 0.07 to 0.10. It will be appreciated that
while phosphoric acid is most preferred, phosphate esters such as
butyl or phenyl acid phosphate and the like are suitable for use as
component (d) in the preparation of compound (I).
[0068] Polymerization of the reactants may occur at typical
esterification conditions, i.e., 200-230.degree. C. reaction
temperature while continuously removing water as a reaction
by-product. Solvents that facilitate the removal of water from the
reaction system (those that form an azeotrope) such as xylenes, may
be used.
[0069] Reactants (a), (b), (c) and (d) will generally be used in a
molar ratio of 4.2:4.9:0.01:0.0005 to 5.1:5.6:0.7:0.005, preferably
from 4.4:5.0:0.02:0.0008 to 5.0:5.5:0.6:0.003, and most preferably
from 4.8:5.2:0.02:0.0009 to 4.9:5.4:0.06:0.002.
[0070] A commercially available and most preferred example of
compound (I) is Borchigen HMP, commercially available from the
Wolff Walsrode division of the Bayer Corporation of Burr Ridge,
Ill., U.S.A.
[0071] Compound (II) comprises a carboxy phosphate ester having the
formula: 2
[0072] wherein M is hydrogen, metal or ammonium, x is a number from
0 to 3, and R is a saturated or unsaturated C.sub.5-C.sub.40
aliphatic group in which one or more of the aliphatic carbon atoms
can be substituted or replaced with a halogen atom (such as
fluorine or chlorine), a C.sub.1-C.sub.6 alkyl group, a
C.sub.1-C.sub.6 alkoxy group, a C.sub.6-C.sub.10 aromatic
hydrocarbon group, preferably phenyl or naphthyl, or a
C.sub.6-C.sub.10 aromatic hydrocarbon group that is substituted
with one or more (preferably 1 to 3) C.sub.1-C.sub.6 alkyl groups
or --COOR.sup.1 groups wherein R.sup.1 is H, metal, ammonium,
C.sub.1-C.sub.6 alkyl, or C.sub.6-C.sub.10 aryl, or mixtures
thereof
[0073] In preferred compounds (II), R will contain one or more
C.sub.6-C.sub.10 aromatic hydrocarbon groups, and most preferably,
one or more C.sub.6-C.sub.10 aromatic hydrocarbon groups which
contain one or more, preferably at least two, --COOR.sup.1 groups
wherein R.sup.1 is H, metal, ammonium, C.sub.1-C.sub.6 alkyl, or
C.sub.6-C.sub.10 aryl.
[0074] In a most preferred compound (II), R will contain at least
one C.sub.6-C.sub.10 aromatic hydrocarbon group and at least two
--COOR.sup.1 groups wherein R.sup.1 is H, metal, ammonium,
C.sub.1-C.sub.6 alkyl, or C.sub.6-C.sub.10 aryl. R.sup.1 will most
preferably be a C.sub.1-C.sub.6 alkyl or a C.sub.6-C.sub.10 aryl
group.
[0075] The --COOR.sup.1 groups may be lateral or terminal. It will
be appreciated that when R.sup.1 is H, compound (II) will comprise
one or more free carboxylic acid groups. Similarly, when R.sup.1 is
a metal or ammonium ion, compound (II) will have one or more
carboxylic acid salt groups. Finally, when R.sup.1 is a
C.sub.1-C.sub.6 alkyl or a C.sub.6-C.sub.10 aryl, compound (II)
will comprise one or more ester groups.
[0076] It will be appreciated that suitable compounds (II) can and
most preferably will comprise mixtures of compounds having the
formula: 3
[0077] wherein R, M, x, and R.sup.1 are as described above.
However, in a most preferred embodiment, such a mixture will
contain one or more molecules having the above structure wherein x
is 1 or 2, preferably 1, R has at least one C.sub.6-C.sub.10
aromatic hydrocarbon group substituted with at least one,
preferably two, --COOR.sup.1 groups wherein R.sup.1 is H or a
C.sub.1-C.sub.6 alkyl or C.sub.6-C.sub.10 aryl, most preferably a
C.sub.1-C.sub.6 alkyl, and M is H.
[0078] Compound (II) will generally have a number average molecular
weight in the range of from 600 to 1200, preferably from 700 to
900, and most preferably from 750 to 850. Compound (II) will
generally have a polydispersity of from 1.00 to 2.00, with a
polydispersity of 1.00 to 1.50 being preferred and a polydispersity
of 1.15 to 1.35 being most preferred.
[0079] Suitable compounds (II) will also have an acid number in the
range of from 50 to 200 mg KOH/g, preferably from 100 to 180 mg
KOH/g, and most preferably from 120 to 160 mg KOH/g. In addition,
suitable compounds (II) will have a hydroxyl number in the range of
from 100 to 250 mg KOH/g, preferably from 120 to 230 mg KOH/g, and
most preferably from 150 to 200 mg KOH/g.
[0080] Suitable compounds (II) generally comprise the reaction
product of (a) at least one difunctional polyol, (b) phosphoric
acid, and (c) at least one trifunctional carboxylic acid.
[0081] Examples of suitable difunctional polyols (a) include
neopentanediol, ethylene glycol, diethylene glycol, propylene
glycol, dipropylene glycol, hydrogenated bisphenol A,
1,6-hexanediol, hydroxypivalylhydroxypivalate,
cyclohexanedimethanol, 1,4-butanediol, 2-ethyl-1,3-hexandiol,
2,2,4-trimethyl-1,3-pentandiol, 2-ethyl-2-butyl-1,3-propanediol,
2-methyl-1,3-propanediol, and mixtures thereof. Preferred
difunctional polyols (a) are neopentane diol and
2-ethyl-2-butyl-1,3-propanediol, with neopentane diol being most
preferred.
[0082] The at least one trifunctional carboxylic acid (c) may be
aromatic or aliphatic in nature, but aromatic containing structures
are most preferred. Examples of suitable trifunctional carboxylic
acids are trimellitic acid, 1,3,5-benzenetricarboxylic acid, citric
acid, and mixtures thereof. Preferred trifunctional carboxylic
acids are 1,3,5-benzenetricarboxylic acid and trimellitic acid,
with trimellitic acid being most preferred.
[0083] Phosphoric acid (c) is as described above with respect to
(I(d)).
[0084] Polymerization of the reactants (a), (b), and (c) may occur
at typical esterification conditions, i.e., 200-230.degree. C.
reaction temperature while continuously removing water as a
reaction by-product. Solvents that facilitate the removal of water
from the reaction system (those that form an azeotrope) such as
xylenes, may be used. The reaction can also be subsequently admixed
with suitable solvents.
[0085] Reactants (a), (b), and (c) will generally be used in a
ratio of 6.3:3.0:0.05 to 7.9:4.0:0.15, preferably from 6.7:3.2:0.07
to 7.6:3.8:0.12, and most preferably from 6.9:3.3:0.09 to
7.3:3.5:0.11.
[0086] A commercially available and most preferred example of
compound (II) is LUBRIZOL.TM. 2063, available from the Lubrizol
Corp of Wickliffe, Ohio.
[0087] Compound (I) will typically comprise from 50 to 80% by
weight of the mixture of compound (I) and compound (II), preferably
from 60 to 75% by weight, and most preferably from 65 to 70% by
weight, based on the total weight of the mixture of compound (I)
and compound (II). Compound (II) will comprise from 20 to 50% by
weight of the mixture of compound (I) and compound (II), preferably
from 25 to 40% by weight, and most preferably from 30 to 35% by
weight, based on the total weight of the mixture of compound (I)
and compound (II).
[0088] The composition comprising the mixture of compound (I) and
compound (II) will typically be present in a coating composition in
an amount of from 0.10 to 1.00% by weight, preferably from 0.10 to
0.30%, and most preferably from 0.15 to 0.25% by weight, based on
the total nonvolatile weight of the coating composition.
[0089] The mixture of compound (I) and compound (II) may
incorporated into finished coating compositions by conventional
mixing techniques using mixing equipment such as a mechanical
mixer, a cowles blade, and the like. Although the additives may be
added during the manufacturing process or subsequently to a
finished coating, those skilled in the art will appreciate that in
a most preferred embodiment, the additives will be added post grind
during the manufacturing process. Although the mixture of compound
(I) and compound (II) may be used in single or two component
systems, use in two-component systems is preferred, particularly
where the mixture of compounds (I) and (II) is placed in the resin
component of a two component system.
[0090] Finally, although a variety of packaging options are
suitable for containing the coating compositions of the invention,
it is most preferred that coating compositions containing the
mixture of compounds (I) and (II) be packaged in epoxy or phenolic
lined cans. Packaging in such containers has been found to ensure
the retention of optimum adhesion characteristics.
[0091] The mixture of compound (I) and compound (II) when used in
coating compositions provides improved adhesion of the coating
composition to bare untreated metal substrates, including aluminum
and galvanized steel substrates.
[0092] The coating compositions of the invention may be stored as
such for prolonged periods at room temperature without gel
formation or undesirable changes. They may be diluted as required
to a suitable concentration and applied by conventional methods,
for example, spraying or spread coating, and cured by exposure to
ambient temperatures of from 70 to 75.degree. F. for a period of
from 1 to 3 hours, preferably from 1.5 to 2 hours. However,
sandable films of the coating compositions of the invention
comprising mixtures of compounds (I) and (II) may also be obtained
upon exposure of the applied coating to temperatures in the range
of from at least 120.degree. F., more preferably up to 140.degree.
F., for periods of from 30 to 50 minutes, preferably from 30 to 40
minutes.
* * * * *